Rheology and Phase Morphology Properties of Recycled Asphalt Modified with Waste Cooking Oil and Activated Crumb Rubber

To improve the performance of hot mix asphalt (HMA) with recycled asphalt pavement (RAP), it is commonly required to incorporate rejuvenators and modifiers to achieve a superior quality of rejuvenated asphalt. However, the potential interaction between the modifier and the rejuvenator is often overlooked during this process. Therefore, in this study, a more appropriate dosage of waste cooking oil (WCO) was selected to rejuvenate aged asphalt while enhancing the content of activated crumb rubber (ACR) in rejuvenated asphalt. The conventional indexes, rheological behaviors and microscopic characteristics of each binder were evaluated by penetration tests, softening point tests, elastic recovery tests, Dynamic Shear Rheometer (DSR) tests, Bending Beam Rheometer (BBR) tests, Fluorescence Microscope (FM) analysis and Fourier Transform Ioncyclotron Resonance (FTIR) analysis. The results indicated that WCO acts as not only a rejuvenator to improve the viscoelastic properties of aged asphalt but also a solubilizer to fully swell the rubber crumb, improving the high-temperature anti-rutting, low-temperature cracking resistance and fatigue performance of modified asphalt. Moreover, ACR dramatically enhances the high-temperature performance of modified asphalt, but it negatively affects the low-temperature performance when the ACR dosage exceeds the asphalt swelling point. Meanwhile, the addition of ACR and WCO significantly alters the phase morphology of asphalt. At appropriate proportions, the phase morphology changes from a continuous asphalt phase with a dispersed polymer phase to two twisting continuous phases. Furthermore, the Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated that the rejuvenated process of the aged asphalt mainly involved physical blending, while the crumb rubber modification process was accompanied by a small amount of chemical reactions. Finally, considering the overall performance of rejuvenated asphalt, the optimum dosage of WCO and ACR were recommended as 10 wt% and 18 wt%, respectively.